A number of quinolone compounds have been developed and proven successful in commerce, attributing to their potent and broad spectrum of antibacterial activities. Included among such quinolone compounds are Norfloxacin, Enoxacin, Ofloxacin, Ciprofloxacin, and so forth.
In recent years, an extensive investigation has been made to develop a novel structure of pyridone carboxylic acid derivatives which have more potent and broad antibacterial activities. Most of such investigation has been focused onto the development of new substituents at 7-position of the quinolone nucleus.
As prior art references which disclose such derivatives, U.S. Pat. No. 4,988,709, European Patent 0 413 455, and Japanese Laid Open Patent Publication 89-56,673 may be mentioned.